RNA interference (RNAi) is a mechanism capable of inhibiting the expression of a gene in a highly specific and efficient manner, in which degradation of the mRNA of a target gene is inhibited by introducing a double-stranded RNA, which comprises a sense strand having a sequence homologous to the mRNA of the target gene and an antisense strand having a sequence complementary to the sense strand, into cells or the like, thereby inhibiting the expression of the target gene. Since it was known that low-molecular-weight RNA (non-coding RNA) that is not translated in C. elegans controls the expression of genes in the developmental stage, it was found that many low-molecular-weight RNAs are present in the C. elegans genome (Fire et al., Nature 391:806-811, 1998). Such low-molecular-weight RNAs have a size of about 25 nucleotides (nt) or shorter and are also called micro RNA (miRNA), and about 200 or more types of miRNAs are present in C. elegans. miRNA was also found in plants, and among low-molecular-weight RNAs (21 to 25 nt), one completely consistent with the sequence of the target gene is called small interfering RNA or siRNA, and one incompletely consistent with the sequence of the target gene is called microRNA or miRNA. Such low-molecular-weight RNA is produced from non-coding RNA upon cleavage by the RNA processing enzyme Dicer, and RNA before cleavage forms a stem-loop structure. Thereafter, the RNA binds to the target gene region, and expression control occurs by the RNA-induced silencing complex (RISC) or the like. A Dicer-like protein (CARPEL FACTORY/SUSPENSOR/SHORT INTEGUMENT) is also present in plants, and in recent years, an RNAi method has been frequently used as a tool for knocking out the expression of a specific gene in various organisms.
Generally, the flowering time of plants is influenced by environmental conditions or is already genetically determined, and most plants have a mechanism by which their flowering time is controlled such that their flowering occurs at a suitable time. This control mechanism of flowering time is influenced by developmental signals within plants, and external environmental factors such as light and temperature (Poething et al., Science, 250:923-930, 1990). Plants are that are sessile organisms are exposed to various environmental stresses, and thus are much influenced by the surrounding environment. Among such environmental stresses, temperature has the greatest influence on plants. There are many known plants that sense low temperature such as freezing temperature and have a wide range of temperature. When plants are exposed to temperature stress such as low temperature, they have a mechanism coinciding therewith. According to a recent report, it can be seen that plants have a clear mechanism that responds to low temperature (Sharm. P et al., Bioessay 27:1048-59, 2005). Many plant mechanisms that respond to a wide range of temperatures are known, and it was recently reported that a minute change in ambient temperature influences the delay of flowering at low temperatures (Fitter et al., Science 296:1689-91, 2002; Cook et al., PNAS 109:9000-5, 2012; Craufurd et al., J. Exp. Bot. 60:2529-39, 2009).
With respect to conventional methods for controlling flowering time, a mechanism that controls flowering time at a temperature 4° C. or below or a temperature of 37° C. or above differs from a mechanism that controls flowering time by a minute change in the ambient temperature ranging from 10° C. to 27° C., and a molecular mechanism that controls flowering time according to a change in ambient temperature has not yet been completely identified.
Accordingly, the present inventors have made extensive efforts to develop a method capable of controlling flowering time by sensing a small change in ambient temperature, from Arabidopsis thaliana, and as a result, have found that the SVP-FLM-β protein complex can control plant flowering by recognizing a change in ambient temperature, thereby completing the present invention.